The invention relates to a method and a device for process management in the production of pulp and/or paper, using at least one measuring device for registering spectral characteristic values at different wavelengths and at least one regulating or controlling device for the operating means used in the production of pulp and/or paper.
EP 0 445 321 A1 discloses a method for the production of pulp in a continuous digester. In the process, a desired pulp quality is prescribed with the aid of a so-called quality measure (Q). Using a process model, the digestion temperature (T*) belonging to the prescribed value of the quality measure (Q*) is prescribed as a main controlled variable. In this arrangement, the process model may be adapted to accommodate changed operating conditions of the pulp digester. For this purpose, it is important that the supplying of wood chips is included as a process variable in the process model, by means of physical characteristic values.
WO 94/20671 A1 describes a method for regulating the production process of cellulose in which the mass density of the wood chips fed as raw material for the process is taken into account and is envisaged to be variable. Corresponding samples of the mass density of wood chips fed into the process are taken into account in a computing unit and are designed to be as a function of the computational results.
Finally, EP 0 590 433 A2 describes a control method for the production of pulp by means of pressure and temperature control, in which the production process is subdivided into two phases. The first phase of the digestion includes the heating up of the suspension of groundwood and digester liquid which is subjected to as high a pressure as possible. The pressure is lowered in the second phase of the digestion which occurs at the final digestion temperature.
In the earlier international Patent Application WO 95/08019 A, which is not a prior publication, a device is proposed for operating an installation specifically for the production of so-called de-inked pulp. The device contains at least one waste paper preparation means which has a dewatering machine or at least a paper machine connected downstream thereof. In this arrangement, a measuring device for registering spectral and/or physical characteristic values of the waste paper suspension, which is fed to the waste paper preparation means or passes through the latter, is already used. Furthermore, regulating or control devices for the operating means of the waste paper preparation means is used there and at least one state analyzer for the waste paper suspension is proposed. The state analyzer is implemented in the form of one or more parallel neural networks. Using the characteristic values of the measuring device, the state analyzer outputs controlled variables for process management to the regulating or controlling devices of the operating means for the waste paper preparation means.
When the above-described device is used, in particular, for the production of de-inked stock, using as large a proportion as possible of waste paper, a problem particularly taken into account is that the quality of the waste paper introduced into the installation fluctuates severely. For example, depending on the respective mixture of the waste paper, it is possible for widely varying proportions of different types of waste papers to be present, for example, colored, illustrated papers, grey newsprint, white papers, contaminated papers, old books, for example including telephone directories, cartons, packages, coated papers and further contaminations of all types. The device previously described in the earlier patent application solves the problems in a satisfactory manner specifically for the production of de-inked pulp.
Furthermore, U.S. Pat. No. 4,886,576 describes an installation for use in the production of paper. Separate units of primary and secondary refiners for beating digest chips are connected downstream of one or more digesters for the production of pulp from chips. In this case, UV absorption measurements are carried out on the digester liquid, or the so-called pulp. Control or regulation signals are derived from the measured values, on one hand for the temperature management of the digester, and on the other hand for the primary refiner stage. It is important in this case to carry out the UV absorption measurements on the digester liquid with a non-solid consistency, in particular on a pulp, since the UV spectrum thereof is influenced by the constituents dissolved out of the wood.
An object of the present invention is to apply the measurement principle of the sort used in the prior art to the production of pulp and/or paper so that it is suitable for feedforward control.
The object is achieved according to the present invention in that, using a measuring device, the spectral characteristic values of at least the starting materials in the production of pulp and/or paper are registered. The starting materials (i.e., either the raw material xe2x80x9cwoodxe2x80x9d or the secondary raw material xe2x80x9cwaste paperxe2x80x9d) continuously pass by the measuring device, which registers the starting materials"" spectral characteristic values.
Within the scope of the invention, neural networks are used in a manner known in the art as state analyzers for evaluating the spectral characteristic values. In particular, it is advantageously possible therewith to derive from the age of the wood and/or from the proportion of respective wood species such controlled variables as are important for the lignin content of the wood. Signals derived in such a way can be used, for example, for controlling the digester, which is necessary for the production of pulp and/or paper.
The associated device for carrying out the method contains at least one measuring device for registering spectral characteristic values and at least one regulating or controlling device for the operating means used. The measuring device may be a spectrometer for registering intensity measured values at different wave-lengths. By suitable evaluation of the measured values, correction variables for the regulating or controlling device may be derived. There can be additional measuring devices in the production line, so that in the same way characteristic values of the intermediate and/or final products can be registered, from which signal variables can be fed back to the controlling or regulating device.